Airbag devices are used to protect occupants in an emergency or a collision of vehicles. For example, an airbag device attached to a steering wheel inflates and deploys an airbag in front of a driver's seat. An occupant in the driver's seat is received and restrained by the airbag in front of the occupant. In a conventionally known airbag device of this type, the inside of an airbag is divided into a plurality of chambers so that the airbag can quickly deploy sideways (see PTL 1).
In the conventional airbag device, a first chamber is delimited by an inner panel at the center of the airbag, and a second chamber and a third chamber are delimited by separation panels around the first chamber. However, in this airbag device, the second chamber and the third chamber sequentially inflate after the first chamber inflates toward an occupant with high-pressure gas generated by an inflator. Hence, at the initial stage of deployment of the airbag, the first chamber may burst out and strike the occupant. This may increase the impact on the occupant. The impact on the occupant is large especially when the occupant is near the steering wheel.
Furthermore, in the conventional airbag device, bursting out of the airbag suddenly stops when the inner panel is fully stretched. The airbag inflates to a thickness corresponding to the length of the inner panel. Therefore, if the inner panel is too long, the distance by which the airbag projects is large, increasing the risk to the occupant. Conversely, if the inner panel is too short, the airbag is thin, failing to receive the occupant. The occupant may collide with the steering wheel. Furthermore, the airbag may bounce as if it expands and contracts in the thickness direction due to a reaction force generated when the inner panel is suddenly stopped.
FIG. 17 includes side views illustrating a bouncing conventional airbag. FIGS. 17A and 17B also illustrate a steering wheel and an occupant colliding with the airbag.
As illustrated in the figures, a conventional airbag 100 may bounce on a steering wheel 90 after it inflates and deploys (arrow W in FIG. 17A). As a result, the shape of the airbag 100 varies between a shape V1 (maximum thickness) and a shape V2 (minimum thickness). Because the shape of the airbag 100 is unstable, the performance of the airbag 100 may be unstable. Furthermore, for example, if an occupant 91 (see FIG. 17B) comes into contact with the airbag 100 in the shape V2 (minimum thickness), the absorbing stroke of the airbag 100 may be insufficient. The absorbing stroke is a stroke of the airbag 100 when absorbing the impact and energy of the occupant 91. Accordingly, from the standpoint of safely restraining the occupant 91, the conventional airbag 100 is required to inflate and deploy in a more stable manner.
Furthermore, in the conventional airbag 100, because a joint portion of the inner panel (not shown) is subjected to a high load, the strength of the joint portion needs to be increased. For example, when the joint is made by stitching, the stitching strength needs to be increased by adding a reinforcing fabric piece, changing the thread size, or changing the stitching shape. Therefore, the conventional airbag 100 has problems of increased manufacturing efforts and costs.